An integral part of any aircraft fuselage is the door assembly through which passengers and crew enter and exit the aircraft. The door assemblies of modern commercial aircraft are designed to stay sealed regardless of the large pressure differential between the interior of the fuselage and the outside environment when the aircraft is in flight at high altitudes. This necessitates providing the door assemblies with relatively heavy locking mechanisms in order to make sure the integrity of the seals is maintained. Moreover, most commercial aircraft door assemblies are provided with an emergency escape chute that can be quickly inflated in the event a rapid evacuation of the aircraft is required. The escape chute further adds to the weight of these door assemblies. Consequently, it is not uncommon for an aircraft door of a modern commercial airliner to weigh 400 pounds or more. Most of these doors are provided with latch mechanisms that employ human energy to first break the door seal and then move the door free of the fuselage opening in which it is disposed. In normal circumstances, flight attendants or ground personnel need only exert themselves for several seconds in order to place a door in the open position.
However, there are instances wherein even the few seconds it regularly takes to open an aircraft door may be too long. These instances are when there is an event, such as cabin fire, that requires all those in the aircraft to leave rapidly for their own safety. It is during these events that it is necessary to deploy the escape chute in order to insure that persons can safely evacuate the airplane even if it is not located near a jetway or a set of boarding stairs. Consequently, both safety considerations and regulatory requirements demand that in emergency situations aircraft doors open rapidly, and the associated escape chutes quickly inflate so that persons can evacuate the aircraft without delay.
As a result of these requirement, the door assemblies of many commercial aircraft are provided with emergency actuators for rapidly moving them free of the aircraft openings to which they are attached. One type of actuator is a gas-driven piston which is linked to a rotating hinge pin to which the door hinge is attached. When the actuator is triggered, the piston moves so as to cause the hinge pin to rotate. Since the hinge is attached to the hinge pin, the rotation of the pin causes the hinge to pivot so as to force the door open. These actuators have proved to be well suited mechanisms for rapidly opening aircraft doors.
Nevertheless, existing actuators have a disadvantage in they necessitate special design considerations for aircraft in which they are installed. These actuators tend to impose relatively large lateral forces on the hinge pins to which they are linked. Consequently, the hinge assemblies must be designed so that they can withstand these forces when the associated actuators are triggered. Similarly, the piston movement imposes an intense mechanical shock on its housing. This necessitates having to securely brace the housing to the fuselage in order to be sure it remains secured when the actuator is triggered. The reinforcing bracing required for the hinge assembly and the actuator housing add to both the weight and the cost of the aircraft. Moreover, the actuators, in combination with the linkage mechanisms used to connect them to the door hinge pins, occupy a significant amount of space. Consequently, installing these actuators in the vicinity of aircraft door assemblies, where it is already necessary to provide a number of different components in a limited amount of space, has proved to be a difficult task.